[Source: CNN Entertainment]

Occasionally a movie gets misleadingly marketed for understandable reasons, and so it is with “IF,” a sweetly sentimental film from writer-director John Krasinski that the ads make look like a madcap romp.

The best parts should strike a mildly receptive chord with parents while potentially boring younger kids, a prescription that could subject the movie’s imaginary friends to a harsh reality once audiences in summer-movie mode get a good look at it.

After his breakout success with “A Quiet Place” (whose delayed prequel will arrive in June), Krasinski shifts toward a PG-rated movie built around animated characters, infused with a family-friendly vibe. Yet it’s no accident that the classic James Stewart movie “Harvey” at one point plays on the TV, since “IF” seeks the same whimsical tone, while owing perhaps its strongest debt to the 1995 film adaptation of “A Little Princess” – which also focuses on a young girl dealing with grief, loss and uncertainty – brightened by detours into the fantastic.

Bea (Cailey Fleming, delivering a splendid anchoring performance after growing up among “The Walking Dead”) has already lost her mom, and now her dad (Krasinski) is hospitalized as he awaits heart surgery. Forced to stay with her grandma (Fiona Shaw), Bea discovers a neighbor (Ryan Reynolds in kinder, gentler mode) who works to find new homes for imaginary friends (or IFs) whose kids have grown up and forgotten them.

The imaginary friends, not surprisingly, turn out to be an eclectic and colorful lot, featuring a wide assortment of celebrity voices, among them Krasinski’s wife, Emily Blunt, and the late Louis Gossett Jr. The most prominent imaginary pair each have notable connections to other cast members: Krasinski’s “The Office” co-star Steve Carell, whose needy Blue bears a too-strong resemblance to McDonald’s Grimace; and Blossom, voiced by Phoebe Waller-Bridge, who produced “Killing Eve,” which co-starred Shaw.

As Bea states at the outset, she no longer considers herself a kid given what she’s endured, which makes the dual mission pretty overt – not just finding kids to go with these eccentric monsters, but helping the girl rediscover the wonders of childhood.

In that latter regard, Krasinski conjures some touching, lovely moments, although they coexist awkwardly with the imperative to wring laughs and sight gags out of the computer-generated characters, which, however impressively they’re rendered, has the effect of flattening the movie.

In one respect, it’s admirable that Krasinski would try to parlay whatever clout he’s amassed into something more heartfelt, but that approach might have fared better by sparing the demands and expectations that go with lining up all those big names, lavish premieres, colorful character posters and marketing tie-ins. Simply put, it’s a tough needle to thread.

“Sometimes, life doesn’t always have to be fun,” Bea somberly tells her dad early on, as he tries to lift her spirits and allay her fears.

“IF” does make the case for finding the fun in life, but in a movie that needs to be more fun than it is.

“IF” premieres May 17 in US theaters. It’s rated PG.